NASA/JPL-Caltech/University of Arizona
Deep under its surface, Mars is quaking. The team behind NASA’s InSight lander, which reached the Martian surface in November 2018, has released the data from its first 10 months. These new measurements show the complexity of the planet, from its atmosphere to deep underground. Here are some of the mission’s most fascinating discoveries so far.
1. Big marsquakes
InSight’s main goal is to measure marsquakes, which can be caused by underground seismic activity or objects hitting the planet’s surface. So far, it has detected 24 relatively major marsquakes of magnitudes between 3 and 4.
These marsquakes occurred deeper underground than most earthquakes, said team member Philippe Lognonné at the University of Paris during a press call. This means that even though they are by no means puny, they would probably be barely noticeable if you were standing on the planet’s surface.
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Two of the quakes occurred near an area called Cerberus Fossae, where the fractured ground indicates there was volcanic activity within the past 10 million years or so. This seismic shaking could come from the remains of that volcanism, said Sue Smrekar at NASA’s Jet Propulsion Laboratory (JPL) in California, also an InSight team member.
InSight has yet to detect any of the truly powerful quakes, though. “The larger quakes at this point seem to be less frequent than we had expected,” says Bruce Banerdt at JPL, the mission’s principal investigator. It isn’t clear why that is.
2. Little marsquakes
The rest of the 174 quakes discovered during InSight’s first 10 months were relatively small, making it harder to figure out exactly where they occurred and what caused them. Since then, the lander has spotted further small marsquakes that weren’t included in this data release.
“We now have about 450 quakes in our catalogue, and those quakes are likely distributed all across the planet and have different mechanisms,” said Smrekar. “Right now, we’ve got a lot more data than we have conclusions, and we’re still trying to get our arms around what Mars is telling us.”
3. Water
The way in which seismic waves propagate through the ground depends on its structure and how hydrated it is, so the quakes can tell us about the distribution of water on Mars. The top layers of crust seem to contain minerals with water in them, said Banerdt.
The crust is drier than Earth’s, but significantly damper than the moon. If InSight finds larger marsquakes from deeper down, they should tell us more about where to find water.
4. Weirdly strong magnetic fields
Mars doesn’t have a constant magnetic field like Earth’s, although it probably did billions of years ago. Instead, it has small areas of magnetic fields caused by rocks that have maintained their magnetisation over the millennia. We have measured some of those fields from satellites, but InSight has the first magnetometer ever placed on the Martian surface.
“We unexpectedly see that there’s a steady field that’s about 10 times stronger than that predicted from satellite observations, and that means that there are magnetised rocks at InSight’s landing site,” said Catherine Johnson at the University of British Columbia in Canada, another InSight team member. These rocks are probably deep underground.
Their ancient magnetisation tells us something about the history of the Martian depths. “If they had been heated up over a few hundred degrees Centigrade, that magnetisation would have been wiped out,” said Johnson. So they must have stayed fairly cool since they became magnetised billions of years ago.
5. Dust devils
The surface of Mars is covered in more dust devils – mini-tornadoes that loft dust into the air – than we thought. So far, InSight has detected more than 10,000 spinning vortices passing over its pressure sensors, said Lognonné. Despite that, it hasn’t taken a single actual picture of a dust devil, which is surprising. That may be because the vortices are simply not strong enough to carry much dust, but it isn’t clear why that would be the case.
Journal reference: Nature Geoscience, DOI: 10.1038/s41561-020-0544-y
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